Giải thích các bước giải:
a.Ta có $OA\perp OM\to\widehat{AOM}=90^o$
$\to\widehat{NOA}=\widehat{NOM}-\widehat{AOM}=30^o$
$OB\perp ON\to\widehat{NOB}=90^o$
$\to\widehat{MOB}=\widehat{MON}-\widehat{NOB}=30^o$
$\to\widehat{AON}=\widehat{BOM}$
b.Ta có $Ox,Oy$ là phân giác $\widehat{AON},\widehat{BOM}$
$\to \widehat{NOx}=\dfrac12\widehat{AON}=15^o,\widehat{MOy}=\dfrac12\widehat{BOM}=15^o$
$\to\widehat{xOy}=\widehat{MON}-\widehat{NOx}-\widehat{MOy}=120^o-15^o-15^o=90^o$
$\to Ox\perp Oy$
